As rubber compositions for tires, such as rubber compositions for bead apexes, base treads or the like, there are used compositions containing large amounts of a vulcanizing agent such as sulfur and a vulcanization accelerator, and a small amount of silica (Patent Document 1). Such rubber compositions disadvantageously have a shorter scorch time, and thus are likely to undergo burning upon being processed. In addition, rubbers obtained by curing the rubber compositions tend to have lower elongation at break. In the case that the rubber compositions are used for base treads and bead apexes, the rubber compositions show only an elongation of about 135%.
In these rubber compositions, the amount of natural rubber and/or isoprene rubber is reduced to about 40 parts by weight and these rubbers are used in combination with a polymer such as modified butadiene rubber, modified styrene-butadiene rubber, or chloroprene rubber; thereby these rubber compositions achieve ultra-high hardness or ultra-low tan δ. However, the elongation at break tends to be lower in the case that the rubber compositions contain a small amount of natural rubber and/or isoprene rubber, a large amount of sulfur, and no silica. In addition, such rubber compositions have a shorter scorch time, and thus require a vulcanization retarder.
Patent Document 1: JP-A 2005-187825